The present invention relates to an image recording apparatus for recording an image on a recording medium using intermediate image sheets each carrying a light shielding image on a light transmissive sheet (hereinafter referred to as "mask members"). More particularly, the invention relates to an image recording apparatus in which the mask member is interposed between a light source and a positive type photosensitive recording medium and light from the light source is irradiated onto the recording medium through the mask member to form thereon a latent image corresponding to the light shielding image of the mask member.
There is a co-pending U.S. patent application Ser. No. 07/175,392 filed by Masashi UEDA et al on Mar. 30, 1988, in which disclosed is an image recording method upon which the present invention is based. In the co-pending application, it is proposed that a color image and a monochromatic image (black image on white background) both provided on an original are recorded on a recording medium so that color displacement of the monochromatic image is obviated. More specifically, as shown in FIGS. 5A through 5D, four mask members 330R, 330G, 330B and 330L are used to record black character images (ABCDEFGH) together with color images as shown in FIG. 5E. In FIGS. 5A through 5D, those designated by 330R, 330G and 330B are half-tope mask members used for reproducing a half-tone image and the one designated by 330L is a fine line mask member used for reproducing fine line images. The half-tone image is reproduced according to a gradation reproducing method, but such a method is not employed when reproducing the fine line image.
Three kinds of half-tone mask members 330R, 330G and 330B are needed, since the image on a half-tone area is recorded by way of color resolution. Light of a wavelength causing to reproduce red color is irradiated onto the recording medium through the mask member 330R. Similarly, lights of wavelengths causing to reproduce green and blue colors are successively irradiated thereonto through the mask members 330G and 330B, respectively. By such a multiplexed exposure, the full-color image is reproduced according to a quasi-gradation method. On the other hand, in order to reproduce the fine line image, the fine line mask member 330L is used in which the half-tone area is wholly masked to prevent light from reaching the recording medium and the lights corresponding to red, green and blue are successively or simultaneously irradiated onto the fine line area to thus expose the recording medium to light through the mask member 330L. By the exposure performed in such a way, a highly resolutive monochromatic image is reproduced without incurring color displacement in the fine line image.
However, the fine line mask member 330L includes a light shielding area covering entirely the half-tone area, while each of the half-tone mask members includes a light shielding area covering entirely the fine line area. Therefore, in the case of reproducing an original in which the fine line area occupies a larger part, a large amount of light shielding material is required to shield the fine line area. When the four mask members are produced by an electrophotographic printer or an ink jet printer, a large amount of toner or ink is used and thus cost for producing one sheet of the mask member becomes costly.